The present invention relates to improvements in rolls for use in corrugated fibreboard production and processing machines.
The roll according to the present invention is intended for use as a rider roll in the gluing portion of a corrugating machine, a weight roll in its heating portion, a feed roll arranged before a rotary cutter, and a feed roll in corrugated fibreboard processing machines such as a printer, a folder-gluer and a rotary die cutter.
Generally, single-faced or double-faced corrugated fibreboards are liable to have their corrugations crushed or deformed when nipped between rolls. This tendency is marked particularly when the liner used is thin.
In the corrugated fibreboard industry, it has heretofore been a large problem to prevent such a deformation of the corrugations, thereby maintaining the thickness of corrugated fibreboard which is its life.
At the gluing portion of a corrugating machine for producing corrugated fibreboards, a glue roll is provided to apply glue to the peaks of the corrugations of a single-faced corrugated fibreboard web fed from the preceding station. Over the glue roll is arranged a heavy rider roll made of steel. The rider roll having its shaft supported by a lever is usually set to lightly press the web against the glue roll to prevent poor gluing due to uneven application of glue.
The rider roll presses the web from its liner side. In addition to unevenness due to some irregularity in the flute height (what is called "high-low") formed during the corrugating process, the liner surface is not even but tends to be lower at the portions facing the bottoms of the corrugations than at the portions facing their peaks. Further, the conventional rider roll contacts the web substantially on a line or tangentially. Therefore, the rider roll is usually set for its bottom to contact the lower portions of the liner or set at an even lower position for secure gluing. The lever mechanism supporting the rider roll is provided with a stopper to prevent the rider roll from lowering from its preset position. The lever allows upward movement of the rider roll but which is too heavy to be moved upwardly. Because the arrangement is such as mentioned above, the corrugations are deformed more or less when the corrugated fibreboard web is nipped between the glue roll and the rider roll.
Also, with the conventional rider roll made of steel, since it has to be set so as to lightly press the web, there is a tendency that a more than necessary amount of glue is applied to the peaks of the corrugations. This results in poor economy and in that the single-faced web absorbs an excessive amount of moisture.
Excessive absorption of moisture is undesirable for the following reasons. Firstly, the corrugated fibreboard web would soften so much owing to excess moisture that it would become more liable to have its corrugations deformed when passed between rolls at succeeding steps.
Secondly, the web would have to absorb a greater amount of heat at the heating portion which comes after the gluing portion. This means a greater loss of heat energy. Also, the web would have to stay at the heating portion for a longer time. This decreases the machine speed and thus the production per unit time. Furthermore, the pressure applied to the web against the heating plates has to be increased for better heat absorption. This also makes the web more liable to have its corrugations deformed.
Thirdly, an excessive amount of moisture makes the corrugated fibreboard web more liable to warp, which might cause machine trouble and produce defective webs.
Whenever the liner used changes, the clearance between the glue roll and the rider roll has to be readjusted. This adjustment is very troublesome and requires a high degree of skill. Readjustment of the clearance is also required when the type of corrugation or flute changes. Therefore, a particular set of a rider roll and a glue roll having the clearance therebetween preadjusted is usually prepared for each type of flute.
At the heating portion of the corrugating machine, a number of weight rolls made of steel are arranged to press the corrugated fibreboard web against the heating plates through a cotton belt for better heat conduction. Each weight roll has its shaft supported by a lever or a wedge adapted to allow adjustment of the pressure applied to the web.
The larger is the pressure applied by the weight rolls to the web, the better is the gluing and the higher is the machine speed which can be expected, but the greater would be the possibility of causing deformation of the corrugations. Since the weight rolls press the web through the cotton belt on a line or tangentially, the pressure applied to the web is considerably large even though the web is pressed not directly but through the cotton belt.
When the joints of the cotton belt where the belt sections are joined as by lacing and its bulging portions where some foreign matter is attached pass under the weight rolls, the rolls will skip, thus applying excessive pressure to the web and causing deformation of its corrugations.
At the heating portion also the clearance between the weight rolls and the heating plates has to be readjusted according to the flute type, material, etc. of the corrugated fibreboard web.
The deformation of the corrugations is most likely to occur at the processes where the web contains a relatively large amount of moisture, i.e. at the glueing portion and the heating portion.
Next, a pair of feed rolls made of steel are arranged upstream of a rotary cutter of the corrugating machine to feed the corrugated fibreboard web toward the rotary cutter. The feed rolls are rotated at a slightly higher speed than the feed speed of the web to feed the web without letting it accumulate before the rotary cutter. Thus, the web is fed to the rotary cutter while being slightly pulled by the feed rolls.
With the conventional steel feed roll, the upper and lower feed rolls contact the corrugated fibreboard web substantially tangentially on a transverse line. Therefore, in order to feed the web while slightly pulling it, the pair of the feed rolls have to nip the web with a considerable pressure, thus causing deformation of the corrugated fibreboard web.
Pairs of steel feed rolls are also used in other corrugated fibreboard processing machines such as a printer, a folder-gluer and a rotary die cutter. On these machines also, deformation of the corrugations can occur owing to the nip force applied by the feed rolls. Also, deformation can occur at auxiliary feed rolls and processing rolls provided in such processing machines.
An object of the present invention is to provide rolls for use in corrugated fibreboard production and processing machines having an elasticity on their outer periphery to prevent deformation of the corrugations without the need of frequent readjustment of the clearance between the rolls according to changes of the material, flute type, etc.